Supercritical water separation process

ABSTRACT

A supercritical water separation process and system is disclosed for the removal of metals, minerals, particulate, asphaltenes, and resins from a contaminated organic material. The present invention takes advantage of the physical and chemical properties of supercritical water to effect the desired separation of contaminants from organic materials and permit scale-up. At a temperature and pressure above the critical point of water (374° C., 22.1 MPa), nonpolar organic compounds become miscible in supercritical water (SCW) and polar compounds and asphaltenes become immiscible. The process and system disclosed continuously separates immiscible contaminants and solids from the supercritical water and clean oil product solution. The present invention creates a density gradient that enables over 95% recovery of clean oil and over 99% reduction of contaminants such as asphaltenes and particulate matter depending on the properties of the contaminated organic material.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.62/359,896, filed Jul. 8, 2016, which is hereby incorporated in itsentirety by reference.

FIELD OF THE INVENTION

The present invention is directed to a supercritical water (SCW)separation process and system for the rapid separation of inorganic andorganic contaminants, such as salts, minerals, metals, asphaltenes,particulate matter, catalyst fines, and coke precursors fromcontaminated organic materials such as petroleum and renewable oils. Theprocess and system is characterized by mixing of supercritical water anda contaminated organic stream, extraction of soluble organicconstituents by SCW, and gravity separation of insoluble contaminants byestablishing and maintaining a density gradient in the separationvessel.

BACKGROUND OF THE INVENTION

Petroleum refiners are continually seeking to improve refinerythroughput and increase the yields of the highest value products,primarily distillate transportation fuels. This is typicallyaccomplished by atmospheric distillation of the lighter components ofpetroleum crude to produce straight-run naphtha, jet, and diesel fuelsthat can be readily hydrotreated to remove sulfur, or undergo furthercatalytic processing to meet gasoline, jet, and diesel fuelspecifications. However, typical petroleum crude oils may contain only40 to 70% straight-run distillate hydrocarbons that boil below 650° F.The goal then is to upgrade the remaining 30 to 60% of atmospheric towerbottoms (ATB) into distillate fuels that boil below 650° F. PetroleumATB contains metals, asphaltenes, and resins that must be removed beforeit is converted into lower-boiling compounds via catalytic hydrocrackingor fluid catalytic cracking (FCC).

Vacuum distillation of ATB is typically employed to produce vacuum gasoil (VGO) distillate and vacuum tower bottoms (VTB) or residuum thatcontains most of the contaminants and exhibits an atmospheric equivalentdistillation temperature greater than about 1000-1050° F. Vacuumdistillation is performed in a manner that VGO produced is sufficientlyreduced in asphaltenes, Conradson Carbon Residue (CCR), and metals topermit upgrading into transportation fuels via catalytic hydrocrackingor FCC. However, only about 80% of refineries have vacuum distillationsystems because they are expensive to build and operate.

The residuum or VTB produced by many refiners still contains valuablehydrocarbons that could be cracked into additional distillate fuels ifasphaltene, CCR, and metal content were reduced to acceptable levels.Solvent deasphalting is a refinery process for extracting asphaltenesand resins from ATB, VTB, or other heavy petroleum fractions to producedeasphalted oil (DAO) that is typically hydrotreated before being fed toFCC or hydrocracking systems. One such commercial process is calledResiduum Oil Supercritical Extraction or the ROSE process practiced byKBR, Inc. The process consists of contacting the feedstock with volatilesolvents, such as propane, butane, or mixtures thereof, in acounter-current extractor at the temperature and pressure needed toprecipitate the asphaltene and resin components that are not soluble inthe solvent. The solvent deasphalting process requires a considerableamount of solvent, and solvent recovery is an energy-intensive process.The yield of DAO is typically only 40-60%. Higher yields can only beobtained by sacrificing DAO quality. Due to the paraffinic nature of thesolvent, paraffins are selectively extracted and recovered in the DAOfraction.

The refining industry would benefit greatly from a process, such as thepresent invention, that will produce high yields (over 90%) of a cleanVGO equivalent from intermediate refinery streams or crude petroleumoil. The clean VGO equivalent is a suitable feed stream forhydrocracking or fluid catalytic cracking due to reduced levels ofasphaltene, CCR, and metals content.

SUMMARY OF THE INVENTION

The present invention includes a process for separating contaminantsfrom a contaminated feedstock includes combining a contaminatedfeedstock and supercritical water to form a supercritical water andfeedstock solution in a hydrothermal separation vessel wherein thehydrothermal separation vessel includes an upper, separation zone, abottom, concentration zone, and a mid-level, mixing zone located betweenthe upper zone and the bottom zone. The process further includesmaintaining a temperature and pressure within the hydrothermalseparation vessel to achieve a vertical density gradient therein suchthat the upper zone of the separation vessel exhibits a lower densitythan the bottom zone of the separation vessel to cause the contaminantsto separate from the solution in the separation zone and to form aproduct stream, removing the product stream from the upper, separationzone of the hydrothermal separation vessel, and removing thecontaminants from the bottom, concentration zone of the hydrothermalseparation vessel.

The present invention also includes a system for separating contaminantsfrom a contaminated feedstock including a feedstock source for supplyinga contaminated feedstock, a water source for supplying water, a heatingdevice for heating the water to supercritical water conditions, and ahydrothermal separation vessel including at least one inlet forreceiving the feedstock and the supercritical water. The hydrothermalseparation vessel includes an upper, separation zone, a bottom zonecomprising a concentration zone, and a mid-level mixing zone locatedbetween the upper zone and the bottom zone. The system further includesa mixing device for combining the contaminated feedstock and thesupercritical water to form a solution, wherein the mixing device ispositioned inline prior to at least one inlet of the hydrothermalseparation vessel or positioned within the hydrothermal separationvessel itself. The hydrothermal separation vessel, feedstock, andsupercritical water cooperate together to achieve a vertical densitygradient within the hydrothermal separation vessel, wherein the upper,separation zone of the separation vessel exhibits a lower density thanthe bottom, concentration zone of the separation vessel to cause thepolar and asphaltic contaminants to separate from the desirable organicsolution in the separation zone and to form a product stream. The systemalso includes at least one outlet for removing the product stream fromthe upper, separation zone of the hydrothermal separation vessel and atleast one outlet for removing the contaminants from the bottom,concentration zone of the hydrothermal separation vessel.

The present invention is a continuous process and system for the removalof metals, minerals, asphaltenes, and resins from a contaminatedfeedstock. Contaminated feedstock (which may or may not be referred toherein as organic) is defined here as any petroleum crude oil, crude oilfraction, refinery intermediate stream, contaminated hydrocarbon, orcontaminated renewable oil including algal oils, pyrolysis oils, orwaste oils and greases. The present invention takes advantage of thephysical and chemical properties of supercritical water (SCW), definedas water above 374° C. and 22.1 MPa to effect the desired separation ofcontaminants from organic materials. At a temperature and pressure abovethe critical point of water (374° C., 22.1 MPa), the desirable nonpolarorganic compounds become miscible in SCW and the undesirable polarcompounds, asphaltenes, and resins become immiscible. Under properconditions, immiscible components and solids will settle via gravity outof the SCW and oil solution. An important property of supercriticalwater is the rapid decrease in the density of SCW with temperature nearthe critical point of water. This relationship is shown in Table 1 forthe temperature range of interest.

TABLE 1 Density of Supercritical Water at 3400 psia (23.44 MPa).Temperature, ° C. Density, Kg/m³ 374 299 380 236 390 165 400 140 410 126

The temperature-density relationship is an important feature of thepresent invention for several reasons that include, but are not limitedto the following: 1) as SCW density decreases, the ratio of the densityof the immiscible constituents to the density of SCW increases which, inturn, increases the settling rate of the immiscible constituents andthus allows for a faster separation rate between the desirable organiccompounds and undesirable polar compounds, asphaltenes, and resins, 2)creation of a vertical density gradient, wherein the highest density isin the bottom, concentration zone and the lowest density is in the upperzone of the separation vessel, creates an inherently stable system whichprevents convective mixing caused by a density inversion (higher densityon the top than on the bottom), 3) the vertical density gradient permitscontinuous up-flow operation wherein SCW-soluble constituents arecontinuously removed with the SCW from the upper zone of the separationvessel and immiscible constituents are continuously removed from thebottom zone of the separation vessel, and 4) the inherently stablenature of the separation vessel, established by the vertical densitygradient that prevents convective mixing, enables scale up tolarger-diameter, higher-volume, commercial-scale systems.

Another feature of the present invention is that the separation vesselprovides an operating environment in which the miscible hydrocarboncomponents are not reactive. Good separation performance is achieved atoperating temperatures only slightly above the critical point of water,i.e., above 374° C., such as in the range of 374 to 400° C. Attemperatures below 400° C., most crude oils and related petroleumfractions, such as ATB and VTB, are not reactive, even as neat,undiluted materials. When these organic materials are highly dispersedin low-density SCW, the potential for undesirable polymerization-typereactions is reduced further. In addition, asphaltene compounds thatconcentrate and are removed from the bottom, concentration zone of theseparation vessel are stable since the temperature in the bottom zone ofthe separation vessel is near the critical point of water. At thistemperature, the bottoms product remains flowable and can be continuallyremoved from the bottom zone of the separation vessel.

This invention has numerous advantages over other cleanup processes suchas solvent deasphalting. Advantages include, but are not limited to: 1)higher yields of VGO equivalent or DAO equivalent product from ATB andVTB; 2) lower yields of asphaltic bottoms material; 3) improved qualityof VGO/DAO (lower metals, CCR, sulfur, and asphaltene content) atequivalent yields; 4) the ability to process oil-water emulsions andco-produce water that is low in total dissolved solids; 5) thereplacement of volatile solvents and solvent recovery systems with waterand oil-water separators; and 6) lower energy requirement thansolvent-based systems where volatile solvents must be vaporized,compressed, and condensed in order to be reused. The process and systemof the invention results in a high yield of product with significantlyreduced concentrations of asphaltenes, resins, organic sulfur, metals,catalysts fines, and minerals, such as silicas, oxides, carbonates,sulfates, and phosphates. The system is specifically desirable for usein processing bitumen, petroleum crude oils, or petroleum fractions suchas ATB, VTB, slurry oil from fluid catalytic crackers, and renewablefats, oils, and greases.

The present invention also has advantages over vacuum distillationbecause selective separation of contaminants is not a function ofrelative volatility or atmospheric equivalent boiling point, but isbased on polarity, solubility in SCW, and density. Therefore,asphaltenes, metals, and heteroatoms can be selectively removed, whichresults in both higher yields of DAO equivalent oil and higher quality,i.e., lower levels of contamination. In addition, selectivity can bemodified by changing separation temperature, the ratio of SCW tocontaminated organic feedstock, or by the addition of separation aids.Separation aids may be organic or inorganic in nature and changeselectivity based on polarity or chemical composition as opposed torelative volatility.

The SCW and oil fraction are cooled, expanded, and separated in aconventional oil-water separator or may be directly fed into ahydrothermal cracking process. The clean oil fraction may be furtherprocessed via conventional catalytic cracking processes such as FCC orhydrocracking. Water recovered from the separator is essentially similarto distilled water and may be recycled without further treatment. Thecontaminant fraction is concentrated in asphaltenes and other polar andnon-soluble contaminants. This fraction may be used without additionaltreating as an asphalt blending component, or it may be converted tocoke and light hydrocarbons via conventional coking processes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an SCW separation system in accordancewith the present invention used for the cleanup of hydrocarbons, whereSCW is pre-mixed with the contaminated organic feed stream prior toentering a separation vessel in a continuous process; and

FIG. 2 is a schematic view of the SCW separation system in accordancewith the present invention used for the cleanup of hydrocarbons, wherethe SCW and contaminated organic feed streams are mixed in the mixingzone of a supercritical water separation vessel in a continuous process.

DESCRIPTION OF THE INVENTION

As used herein, unless otherwise expressly specified, all numbers, suchas those expressing values, ranges, amounts, or percentages may be readas if prefaced by the word “about”, even if the term does not expresslyappear. Any numerical range recited herein is intended to include allsub-ranges subsumed therein. Plural encompasses singular and vice versa.When ranges are given, any endpoints of those ranges and/or numberswithin those ranges can be combined with the scope of the presentinvention. “Including”, “such as”, “for example”, and like terms mean“including/such as/for example but not limited to”.

For purposes of the description hereinafter, the terms “upper”, “lower”,“right”, “left”, “vertical”, “horizontal”, “top”, “bottom”, “lateral”,“longitudinal”, and derivatives thereof shall relate to the invention asit is oriented in the drawing figures. However, it is to be understoodthat the invention may assume various alternative variations, exceptwhere expressly specified to the contrary. It is also to be understoodthat the specific devices illustrated in the attached drawings, anddescribed in the following specification, are simply exemplaryembodiments of the invention. Hence, specific dimensions and otherphysical characteristics related to the embodiments disclosed herein arenot to be considered as limiting. Like reference numerals refer to likeelements.

It should be understood that any numerical range recited herein isintended to include all sub-ranges subsumed therein. For example, arange of “1 to 10” is intended to include any and all sub-ranges betweenand including the recited minimum value of 1 and the recited maximumvalue of 10, that is, all sub-ranges beginning with a minimum valueequal to or greater than 1 and ending with a maximum value equal to orless than 10, and all sub-ranges in between, e.g., 1 to 6.3, or 5.5 to10, or 2.7 to 6.1.

In one embodiment, the present invention includes a process forseparating contaminants in petroleum or other hydrocarbon feedstockscomprising: combining a contaminated organic feedstock with SCW to forma contaminated feedstock and SCW solution; subjecting the solution toSCW conditions in a hydrothermal separation vessel without conversionvia thermal degradation or cracking reactions of the feedstock;maintaining a vertical density gradient in the separator; maintaininglaminar, up-flow conditions such that immiscible contaminants areseparated by gravity from the SCW and feedstock solution; continuouslyremoving clean organic product and SCW from the upper, separation zoneof the separation vessel; continuously removing immiscible contaminantsfrom the bottom, concentration zone of the separation vessel; andcooling and separating clean organic product from the processed SCW. Thedensity gradient in the hydrothermal separation vessel may result inplug flow therein, thereby preventing back mixing or eddy currents. Theresulting clean organic product stream has a lower concentration oforganic and inorganic contaminants than the contaminated organic stream.The organic feedstock may be premixed with SCW before feeding to theseparation vessel or each stream may be delivered separately to amid-level mixing zone in the separation vessel. The separation vesselmay include at least three functional zones: 1) an upper, separationzone, 2) a mid-level, mixing zone, and 3) a bottom, concentration zone.The temperature in the concentration zone is maintained below a reactiontemperature of the contaminants and above a pour point temperature ofthe contaminants. The separation process does not cause molecularrearrangement of hydrocarbon structures such as that which occurs duringthermal cracking, fluid catalytic cracking, hydrocracking,isomerization, cyclization, hydrogenation, or dehydrogenation reactions.These conversion processes may be performed downstream of the system ofthe present invention, thereby benefiting from conversion of cleanfeedstock and reducing or eliminating the problems associated withconversion of contaminated feed stocks.

The separation process is accomplished by creating and maintaining adensity gradient in the SCW separation vessel. The density gradientresults in lower density material present in the upper, separation zoneof the separation vessel and higher density material present in thebottom, concentration zone of the separation vessel. The densitygradient is maintained directly or indirectly by a combination oforganic feed properties and SCW properties in the separation vessel.Separation of miscible components from immiscible components occurs inthe upper, separation zone, which is maintained above the critical pointof water, 22.1 MPa and 374° C. Concentration of the immisciblecomponents occurs in the bottom, concentration zone in or near thebottom of the separation vessel, which may or may not be maintained atSCW conditions. The mid-level, mixing zone exists in the separationvessel at a location that is below the upper, separation zone and abovethe bottom, concentration zone. The mixing zone is maintained above thecritical point of water (374° C., 22.1 MPa).

Operating parameters of the separation vessel are controlled in a mannernecessary to achieve the desired separation. These parametersinclude: 1) the ratio of water-to-oil, 2) the average vertical velocityor hydraulic residence time, 3) the temperature of the separation zone,4) the pressure in the separation vessel, and 5) the nature ofseparation aids. System pressure affects the density of the processfluid that, in turn, affects the hydraulic residence time andcontaminant settling rate. The separation can be performed at anypressure above the pressure of SCW (22.1 MPa). However, generally thereis no practical benefit to operating at pressures greater than 27 MPa.It can be appreciated that specific operating conditions that arenecessary to achieve optimal separation for a given contaminated organicmaterial are dependent on its properties such as: 1) American PetroleumInstitute (API) gravity, 2) chemical nature (paraffinic, naphthenic, oraromatic character), 3) asphaltene content, 4) resin content, and 5)fraction that has an atmospheric equivalent boiling temperature above1000° F. (538° C.). The resins referred to above are typically highmolecular weight compounds that act as a surfactant (with a polar and anon-polar end) that usually associate themselves with asphaltenes andkeep the asphaltenes in solution in crude oil.

Optimal supercritical water-to-oil ratio depends on the level ofcontamination and the nature of the contaminated organic material. Forinstance, it can be appreciated that a higher water ratio may berequired for deasphalting oil containing 10% heptane insoluble compounds(asphaltenes) than for oil containing only 1.0% heptane insolublecompounds. The typical range of SCW-to-oil ratio is between 1:10 to 3:1.Effective separation of asphaltenes is achieved at SCW-to-oil ratiosbetween 1:5 and 1:1.

The net average vertical velocity in the separation vessel must be lessthan the gravity settling rate of the contaminants of interest. Thevertical velocity is determined by the diameter of the separationvessel, the feed rate of SCW and contaminated organic feed streams, andthe operating temperature and pressure. Vertical velocities rangebetween 0.1 and 10 feet per minute (0.03 and 3 meters per minute). Itcan be appreciated that different contaminants exhibit differentsettling rates at a given set of operating conditions. However, for agiven separation vessel, set of operating conditions, and specificcontaminated organic feedstock, the actual settling rate can bedetermined empirically for each of the contaminants of interest.Vertical velocities between 0.5 and 6.5 feet per minute (0.15 and 2.0meters per minute) provide effective separation for most contaminants ofinterest. The hydraulic residence time is a function of the verticalvelocity and the height of the separation vessel. Increasing hydraulicresidence time at a given vertical velocity increases time forcontaminant separation in the separation vessel.

Temperature of the separation vessel is maintained by controlling thetemperature, flow rate, and location of introduction of the contaminatedfeedstock and SCW control streams into the separation vessel. Directcontact of the contaminated feedstock and SCW control streams is onemethod for controlling temperature. The temperature also can becontrolled by indirect means such as heat exchangers or external heatingmethods applied to the separation vessel. However, indirect heating canbe less efficient due to insufficient heat transfer properties exhibitedby SCW that is not mixed or in turbulent flow. The temperature and otherconditions necessary to maintain the density gradient and to preventconvective mixing is dependent on the size of the separation vessel andthe properties of the contaminated feed. A temperature gradient may beused to create a density gradient for some applications. The temperaturegradient is achieved via establishing a difference between thetemperature at the top of the upper, separation zone and the temperatureof the mid-level, mixing zone. The minimum temperature of the mid-level,mixing zone is the critical temperature of water, 374° C. However, thetransition from sub critical water to SCW actually occurs over a rangeof temperatures from several degrees above to several degrees below thecritical point of water. Product temperatures that are significantlyhigher than 400° C. may lead to thermal cracking of the clean organicproduct depending on the thermal stability of the product. Thetemperature in the separation zone thus may be in the range of 380° C.to 450° C., but at most up to the highest temperature that can beachieved without causing thermal cracking, coking, or reaction of thefeedstock.

Contaminated organic feedstock may be any petroleum crude oil, crude oilfraction, refinery intermediate stream, contaminated hydrocarbon, orcontaminated renewable oil. Refinery intermediate streams may includeatmospheric tower bottoms (ATB), vacuum tower bottoms (VTB), and/orfluid catalytic cracker (FCC) slurry oil bottoms. Other hydrocarbonstreams may include bitumen, tar sands, shale oil, coal liquids, usedmotor oil, or mixtures thereof. Renewable feed streams may includelipids; waste fats, oils, and greases; soaps; algae and/or algal oil;and pyrolysis oil. It can be appreciated that other types ofcontaminated feedstock may be separated by the process and system of thepresent invention.

Contaminants that are removed include inorganic materials, such ashalides (e.g., Cl, Br, I), phosphorus and phosphorus-containing species,alkali metals and metalloids (e.g., B, Na, K, Si), and other metals(e.g., Ca, Fe, Mg, Ni, V, Zn). Organic contaminants that are removedinclude asphaltenes, resins (e.g. high molecular weight compounds thatact as a surfactant with a polar and non-polar end that usuallyassociated themselves with asphaltenes and are credited with keepingasphaltenes in solution in crude oil), polymers, high molecular weightpolycyclic aromatic hydrocarbons (PAHs), and coke precursors. It can beappreciated that it may be desirable to recover the resins with theproduct or to dispose of the resins, along with the asphaltene fraction.It can also be appreciated that the resins discussed above do notinclude C5 and C9 resins, which are commercially produced for a varietyof applications. Organic heteromolecules that are partially removedinclude organically-bound sulfur, nitrogen, and oxygen compounds. Thedegree of heteromolecule reduction is dependent on the chemical andphysical properties of the contaminated organic feed and the molecularweight and polarity of the heteromolecule. Particulate matter that isremoved includes coke, mineral and mineral particulates, salts, catalystfines, cellulose, and lignocellulose.

Concentrated contaminants are removed from the bottom of the separationvessel. Depending on the quality of hydrocarbon feed, the yield of theconcentrated contaminant stream may be limited to less than 5 wt. % to10 wt. %. Concentrated contaminant stream properties may be controlledby increasing or decreasing contaminant stream yield relative to productyield to permit direct use of the contaminant stream as an asphalt blendstock, or the contaminant stream could be converted to coke andlow-molecular-weight hydrocarbons via commercial coking processes.

The clean organic product exiting the separation vessel has sufficientlylow metals and asphaltenes content to permit conversion into distillatefuels via catalytic hydrotreating, hydrocracking, hydrothermal cracking,or fluid catalytic cracking. The contaminants may be reduced to lessthan 0.05 wt. % asphaltene, less than 0.05 wt. % ash, and less than 20ppm metals total, i.e., over 99% reduction of contaminants such asasphaltenes and particulate matter. The yield of clean organic productmay be greater than 90% or even 95% depending on the quality ofcontaminated organic feed. Separation aids may be used to selectivelyenhance the separation and recovery of high molecular weight,non-paraffinic hydrocarbons by increasing solubility in supercriticalwater. Separation aids may also be used to selectively enhance theremoval of polar contaminants. Separation aids may be introduced via thecontaminated organic feed, the SCW feed, or as a separate feed stream. Aparticular separation aid can be selected based on the chemical make-upof the feedstock being used and is selected to chemically react with thefeedstock being dissolved in the supercritical water so as to create amore favorable environment for dissolving “like” molecules that have ahigh molecular weight and may not otherwise be soluble in supercriticalwater. For example, the use of xylene as a separation aid could“extract” more high molecular weight aromatic compounds in the SCWphase. Even though asphaltenes are soluble in xylene, xylene will notimprove the solubility of asphaltenes in SCW. Other examples ofseparation aids are cycloparaffin compounds, when used with highlynaphthenic crude oils, or compounds like tetralin that have botharomatic and napthenic character. The separation aids should have a lowboiling point relative to the ATB or VTB contaminated oil and can beeasily recovered and reused. Also, separation aids can be used todecrease the SCW solubility of some constituents in the contaminated oilby the creation of a higher molecular weight or more polar complexesthat would not be soluble in SCW. Examples include compounds that cancomplex with resins, or sulfur compounds. These types of separation aidscan be organic, inorganic, materials such as salt compounds, or weakacids and may be useful when treating renewable oils or waste soaps.Process water recovered with the clean organic product is essentiallysimilar to distilled water and may be reused without further treatment.It can be appreciated that either the clean hydrocarbon and SCW streamor the concentrated contaminant stream from the SCW separation systemmay be directly coupled to any downstream conversion system to minimizeenergy requirements by eliminating additional cooling, heating, andpumping operations.

Reference is now made to FIG. 1, which shows a schematic view of thesystem, generally indicated as 100, in accordance with the invention forthe cleanup of hydrocarbons where supercritical water is pre-mixed withthe contaminated organic feed stream in a continuous process. Theprocess and system of the present invention includes providing ahydrocarbon or petroleum-based contaminated feedstock 150. Thecontaminated feedstock 150 may be fed into an equalization tank 152.Generally, an equalization tank acts as a holding tank that allows forequalization of the flow of the feedstock. An equalization tank can alsoact as a conditioning operation where the temperature of the feedstockis controlled to maintain desired flow characteristics. The contaminatedfeedstock exits the equalization tank 152 at a location 154 and entersinto a pump 156 to form a pressurized feed stream 158. The pressurizedfeed stream 158 may be partially and indirectly heated by afeed-effluent heat exchanger 160 to form a partially heated organicstream 162. It can be appreciated that the feed-effluent heat exchanger160 can be any combination of heat exchangers configured throughout theprocess to maximize overall thermal efficiency. The partially heatedorganic stream 162 may be heated further to the desired processtemperature by any heating device, such as a furnace 164, to form aheated feed stream 166.

A water feed stream 104 can be supplied from an equalization tank 102and fed to a pump 106 to form a pressurized water stream 108 (abovecritical pressure of water). The pressurized water stream 108 may bepartially heated by a feed-effluent heat exchanger 110 to form apartially heated water feed 112. Water feed 112 can be heated to thedesired process temperature by any heating device, such as a furnace114, to form a SCW stream 116. Part of the SCW stream 116 is diverted toa stream 120. Stream 120 may be further split into one or more controlstreams such as 122, 124, and 126. Control valves 132, 134, and 136control the flow of streams 122, 124, and 126 through inlets 122 a, 124a, and 126 a into a hydrothermal separation vessel 170 located alongdifferent vertical heights H of the hydrothermal separation vessel 170.The hydrothermal separation vessel includes an upper, separation zone170 a, a mid-level, mixing zone 170 b, and a bottom portion 170 ccomprising a concentration zone 170 d. The mixing zone 170 b is locatedbetween the upper zone 170 a and the bottom zone 170 c/concentrationzone 170 d.

The flow of each stream is controlled in a manner that maintains thedesired temperature and density gradient in the hydrothermal separationvessel 170. It can be appreciated that stream 120 may be fed directly tovessel 170 or may be split into any number of control streams necessaryto maintain desired operating conditions. By way of example, controlstreams 122, 124, and 126 are either directly injected into theseparation vessel 170 thereby controlling the temperature in theseparation vessel 170 or may be used to indirectly control temperatureby means such as heat exchangers or heat jackets (not shown).

The remainder of SCW stream 116, stream 118, is pre-mixed withcontaminated hydrocarbon feed stream 166 to form a solution stream 168of SCW and hydrocarbon before being fed via at least one inlet 168 ainto the separation vessel 170. It can be appreciated that the SCWstream 118 and contaminated hydrocarbon feed stream 166 are essentiallymiscible and may be mixed by any conventional means at 119 by mixingvalves, static mixers, or simple tee connections to form solution stream168. It can also be appreciated that SCW stream 116 can be heated totemperatures higher than the operating temperature of separation vessel170 to provide additional heat to the contaminated hydrocarbon feedstream 166 and the separation vessel 170. Operation in this mannerreduces the temperature of heated hydrocarbon stream 166 and minimizesthe potential for thermal degradation of hydrocarbon feed streams thatare thermally unstable due to olefin content or contaminants present.Solution stream 168 may be introduced into the separation vessel 170 atany location that is necessary to achieve separation and settling ofimmiscible contaminants. The solution stream 168 may be distributedvertically or horizontally in separation vessel 170 by any distributiondevice 171, such as an eductor or manifold.

Separation vessel 170 provides for the upper, separation zone 170 a tobe above the distribution device 171 and the settling or concentrationzone 170 d below the point where solution stream 168 enters separationvessel 170 via the distribution device 171. The location of thedistribution device 171 within separation vessel 170 may be adjusted inrelation to the upper zone 170 a, mid-level zone 170 b, and bottom zone170 c/concentration zone 170 d of the separation vessel 170, location ofcontrol streams 122, 124, 126, as needed based on the feedstockcomposition, water to organic ratio, vertical flow velocity,temperature, and pressure. The dimensions of separation vessel 170 andthe combined feed rates of streams 168 and 120 (if used for directheating) are controlled to result in a vertical velocity that is lessthan the gravity settling rate of the immiscible organic and inorganiccontaminants of interest at specific operating conditions. The upper,separation zone 170 a is maintained above the critical point of waterand exhibits a vertical density gradient where the density is lower atthe top of the vessel and higher toward the bottom of the vessel. Theupper, separation zone 170 a of separation vessel 170 is maintainedbelow the temperature that would cause thermal degradation of thehydrocarbon stream dissolved in SCW. A product stream 177, from whichthe contaminants have been separated, is continually removed from atleast one outlet 177 a at the top of separation vessel 170. Productstream 177 is a solution of SCW and clean miscible hydrocarbons.

Immiscible contaminants separate from the clean hydrocarbon and SCWsolution and concentrate in the bottom, concentration zone 170 d ofseparation vessel 170. As contaminants settle and concentrate, they arecontinually removed from the concentration zone 170 d as a contaminantstream 172 via at least one outlet 172 a. Contaminant stream 172 mayconsist of asphaltenes, sulfur and nitrogen-containing heteromolecules,feed hydrocarbon, supercritical water, subcritical water, otherimmiscible contaminants, any combination of the above, and suspendedparticulate matter that may consist of catalyst fines, carbon, minerals,or salts. Contaminant stream 172 may be partially cooled by a heatexchanger 173, and is controlled at a temperature sufficient to maintainrelatively low viscosity and good flow characteristics of a stream 174.The flow rate of stream 174 is controlled by a flow control device 175in a manner that maintains steady-state performance of separation vessel170 and minimizes the loss of hydrocarbon feed. It can be appreciatedthat flow control device 175 may be any type of device such as abackpressure regulator, flow control valve, or block-valve system.

Product stream 177 is fed to feed-effluent heat exchanger 110 and formspartially cooled stream 178. Stream 178 is fed to feed-effluent heatexchanger 160 and is cooled further to form a stream 179. Stream 179passes through a pressure control device 180 to form a low-pressureproduct stream 182. It can be appreciated that pressure control device180 may be any type of device such as a backpressure regulator, flowcontrol valve, orifice, or capillary system. Low-pressure product streammay be cooled further by a low-pressure heat exchanger 184 to achievethe desired temperature of a product stream 186 for oil-waterseparation. The cooled product stream 186 is fed to an oil-waterseparator 188 to be separated into streams of a clean organic product192 and a water product 190. Rapid and complete separation of the oiland water phases occurs in oil-water separator 188 because polarconstituents in the contaminated organic feed 150, which could lead tothe formation of emulsions, have been removed from the clean organicproduct 192. Polar, water-soluble impurities have also been removed fromthe product water stream 190 resulting in very low total dissolvedsolids and the ability to reuse recovered water without furthertreatment.

Reference is now made to FIG. 2, which is a schematic view of asupercritical water separation system 200 in accordance with theinvention for the cleanup of hydrocarbons where the SCW and contaminatedhydrocarbon feed streams are mixed in the mixing zone of a SCWseparation vessel in a continuous process. This system is similar to theembodiment shown in FIG. 1, but mixing the SCW with the contaminatedhydrocarbon stream is accomplished internally within the separationvessel 270 versus externally as accomplished by mixing device 119. Thesystem 200 includes a feed system as shown in FIG. 2 for providing acontaminated organic feedstock 250, fed into an equalization tank 252,then fed via a stream 254 to a high-pressure pump 256 to form apressurized organic stream 258. Stream 258 is then partially heated by afeed-effluent heat exchanger 260 and then heated to the desired processtemperature by a heating device 264, which can be any heating device,such as a fired furnace, to form a heated hydrocarbon feed stream 266.

In a like manner, the water feed for system 200 is analogous to thewater feed for system 100. Water 204 from an equalization tank 202 isfed to a pump 206 to form a pressurized water stream 208. Water stream208 is feed to a feed-effluent heat exchanger 210 to form a partiallyheated water stream 212. Water stream 212 is heated to a desired processtemperature by any heating device, such as a furnace 214, to form an SCWsteam 216. It can be appreciated that SCW stream 216 can be heated totemperatures higher than the operating temperature of a separationvessel 270 to provide additional heat to hydrocarbon feed stream 266 andthe separation vessel 270.

A portion of the SCW stream 216 is diverted to a stream 220. Stream 220may be further split into one or more control streams such as 222, 224,and 226. Control valves 232, 234, and 236 control the flow of streams222, 224, and 226 through inlets 222 a, 224 a, and 226 a to vessel 270.A remainder of the SCW stream 218 can be fed into vessel 270 via atleast one inlet 218 a. The flow of each stream is controlled in a mannerthat maintains the desired temperature in separation vessel 270. It canbe appreciated that stream 220 may be split into any number of controlstreams necessary to maintain desired operating conditions. Controlstreams 222, 224, and 226 are used to control the temperature in vessel270 by either direct injection into vessel 270 or by indirect means suchas heat exchangers or heat jackets.

In system 200, SCW and contaminated hydrocarbon streams are not premixedbefore entering separation vessel as was shown for system 100. In system200, mixing takes place in a mixing zone 271 internal to separationvessel 270. It can be appreciated that SCW streams 218, 222, 224, and226, and indirectly heated hydrocarbon feed stream 266 are essentiallymiscible and may be mixed by any conventional means in the mixing zone271. Mixing of streams 218, 222, 224, and 226 with feed stream 266 mayfurther directly heat the contaminated feedstock. As with location ofdistribution device 171 in system 100, it can also be appreciated thatthe heated hydrocarbon feed stream may be introduced into hydrothermalseparation vessel 270 at any location and that the specific location ofmixing zone 271 in vessel 270 can by adjusted to accommodate differentcontaminated feedstocks and operating parameters. The hydrothermalseparation vessel 270 comprises an upper, separation zone 270 a and 270b, and a bottom, concentration zone 270 c, including a contaminant orsettling zone 270 d. The mixing zone 271 may include distributionmanifolds or other mechanical devices and/or shear or turbulent mixinginduced by SCW and hydrocarbon feed stream contact. Benefits of in-situmixing may include: 1) reduced mixing temperature of the contaminatedorganic feed and SCW, 2) reduced preheat requirements for thecontaminated organic feed, 3) reduced likelihood that the less-stableconstituents of the contaminated hydrocarbon feed will undergo thermaldegradation before contacting supercritical water, 4) reduced likelihoodthat insoluble constituents of the contaminated organic feed willprematurely precipitate from solution and foul feed or transfer lines,5) creation of a larger mixing zone with improved mixing that isespecially beneficial when scaling up to larger systems, and 6) theability to change the physical parameters of the mixing zone to improveperformance based on the properties of the contaminated organicfeedstock.

Products from system 200 are recovered in the same manner as wasaccomplished in system 100. Contaminant stream 272 exits the separationvessel 270 via an outlet 272 a and is partially cooled by a heatexchanger 273, but controlled at a temperature sufficient to maintainrelatively low viscosity and good flow characteristics of a stream 274.The flow rate of stream 274 is controlled by a flow control device 275in a manner that maintains steady-state performance of separation vessel270 and minimizes the loss of hydrocarbon feed. Properties of aconcentrated contaminant stream 276 may be controlled to permit directuse as an asphalt blend stock or may be converted to coke andlow-molecular-weight hydrocarbons (not shown) via commercial cokingprocesses.

Product stream 277, from which the contaminants have been removed, exitsthe separation vessel 270 via one or more outlets 277 a and is fed tofeed-effluent heat exchanger 210 to form a partially cooled stream 278.Stream 278 is fed to feed-effluent heat exchanger 260 and is cooledfurther to form a stream 279. Stream 279 passes through a pressurecontrol device 280 to form a low-pressure product stream 282.Low-pressure product stream 282 may be cooled further by a low-pressureheat exchanger 284 to achieve the desired temperature of a productstream 286 for oil-water separation. The cooled product stream 286 isfed to an oil-water separator 288 to be separated into streams of aclean organic product 292 and a clean water product 290.

The following examples are presented to demonstrate the principles ofthe present invention. The invention should not be considered as limitedto the specific examples presented.

EXAMPLES Example 1. Atmospheric Tower Bottoms (ATB) Separation

A bench-scale separation system was configured as shown in FIG. 1. Inthis configuration, SCW 118 and contaminated oil 166 were mixed at teeconnection 119 immediately before being fed into the separation vessel170. A control stream of SCW 126 was also fed at location 126 a intoseparation vessel 170 just below the mixing zone. The inside diameter ofthe bench-scale separation vessel was 2.8 cm (1.1 inches) and the heightof the vessel was 1.65 meters (65 inches). The contaminated organic feedoil was an atmospheric tower bottoms (ATB) from a refinery in theintermountain west. This particular ATB had been previously treated in aROSE solvent deasphalting system so it exhibited relatively lowasphaltene content. However, this ATB did contain metals, sulfur, andhad a relatively high Conradson Carbon Residue (CCR).

The bench-scale separation system was operated with continuous flow ofATB, mix water, control water. Overhead product water and clean oil 177were continuously removed at location 177 a. The concentratedcontaminants 172 were continually removed from the bottom of theseparation vessel at location 172 a. After cooling and expansion ofproduct stream 186 across pressure control valve 180, it was separatedby gravity in oil-water separator 188 and product 192 was recovered foranalysis. The basic operating parameters are summarized in Table 2.

TABLE 2 Operating Parameters Parameter Value Oil feed (166) rate, ml/min38 Mix water (118) rate, ml/min 35 Control water (126) rate, ml/min 25Total water feed rate, ml/min 60 Water-to-oil ratio, volume basis 1.58Vessel operating pressure, psig/MPa 3330/22.96 Mixing zone temperature,° C. 404 SCW density in the mix zone, kg/m³ 128 Vertical velocity atoperating Temperature & 1.07 Pressure, m/min

Product oil 192 and water 190 phases separated rapidly and completelywith no “rag” layer formation. Feed and product properties aresummarized in Table 3. A significant improvement in the productproperties was obtained. API gravity of the contaminated ATB wasincreased by 4.6 degrees. Viscosity was reduced from 144 cSt at 60° C.to 28 cSt at 50° C. Sulfur was reduced by 37%. CCR and ash content werereduced to near zero. Metals content was reduced to 0.1 ppm or less foreach metal tested with the exception of nickel and vanadium, which wasreduced by 90% to 0.5 ppm. The supercritical water separation processshowed a significant improvement in the quality of ATB that had beenpreviously deasphalted by the ROSE process.

TABLE 3 ATB contaminated feed and Clean Product Properties Property ATBFeed Product Specific Gravity, g/cc 0.885 0.860 API, degrees 28.4 33.0Viscosity, cSt @60 C. 144 Viscosity, cSt @50 C. 28 Heptane Insolubles,wt % 0.042 0.032 Conradson Carbon Residue, wt % 2.42 0.11 Sulfur, mg/kg676 426 Ash, wt % 0.019 <0.001 Metals, mg/kg Ca 1.4 <0.1 Mg 0.4 0.1 Na7.1 <0.1 K 0.1 0.1 Fe 12.8 <0.1 Ni 1.8 1.3 V 4.9 0.5

Example 2. Canadian Bitumen Separation

A bench-scale separation system was configured as shown in FIG. 1. Inthis configuration, SCW 118 contaminated organic feed oil 166 andcontrol SCW 126 were delivered to the separation vessel in the samemanner as Example 1. The contaminated organic feed oil was Canadianbitumen that was produced by the SAGD process (Steam-Assisted, GravityDrain). In the SAGD process, steam is pumped into the bitumen-containinggeologic formation and a hot slurry of water and bitumen is recovered.Water had been previously removed from this sample of bitumen. However,the supercritical water separation system is capable of processing thebitumen and water slurry without the need to separate the water. Thedensity and viscosity of most Canadian bitumens are too high to permittransporting by pipeline without extensive upgrading. The purpose ofthis example was to demonstrate that the present invention can reducethe density and viscosity of the bitumen to meet pipeline requirements.

The bench-scale separation system was operated with continuous flow ofneat bitumen, mix water, control water. The bitumen was heated to atleast 80° C. to lower its viscosity and permit effective pumping.Overhead product water and clean oil were continuously removed in thesame manner as Example 1 and the organic product was recovered foranalysis. The basic operating parameters for the Canadian bitumenseparation are summarized in Table 4.

TABLE 4 Operating Parameters for Canadian Bitumen Separation ParameterValue Oil feed (166) rate, ml/min 84 Mix water (118) rate, ml/min 20Control water (126) rate, ml/min 20 Total water feed rate, ml/min 40Water-to-oil ratio, volume basis 0.48 Vessel operating pressure,psig/MPa 3375/23.27 Mixing zone temperature, ° C. 400 SCW density in themix zone, kg/m³ 138 Vertical velocity at operating Temperature & 1.20Pressure, m/min

Product oil and water phases separated rapidly and completely with no“rag” layer formation. The bitumen feed and product properties aresummarized in Table 5. A significant improvement in the productproperties was obtained. API gravity of the contaminated bitumen feedwas increase from 8.6 to 21.9. Pipelines require the API gravity to begreater than 19.0. Viscosity was reduced from 2030 cSt at 60° C. to 18.8cSt at 40° C. 18.8 cSt at 40° C. is equivalent to about 75 cSt at 15°C., which is well below typical the pipeline requirements of less than350 cSt between 7.5 and 18.5° C. depending on the season. The asphaltenecontent, as measured by n-heptane insolubles, was dramatically reducedby 99.5%. The supercritical water separation process showed thatlow-asphaltene, pipeline-quality oil can be produced from Canadianbitumen by the present invention.

TABLE 5 Bitumen Feed and Clean Product Properties Property Bitumen FeedProduct Specific Gravity, g/cc 1.01 0.922 API, degrees 8.6 21.9Viscosity, cSt @60° C. 2030 (measured) Viscosity, cSt @40° C. 18.8(measured) Viscosity, cSt @15° C. (derived) ~75 Heptane Insolubles, wt %8.77 0.045

CLAUSES

The present invention is also directed to the following clauses:

Clause 1: A process for separating contaminants from a contaminatedfeedstock comprised of combining a contaminated feedstock andsupercritical water to form a supercritical water and feedstock solutionin a hydrothermal separation vessel, said hydrothermal separation vesselincluding an upper separation zone and a bottom concentration zone;maintaining a temperature and pressure within the hydrothermalseparation vessel to achieve a vertical density gradient therein suchthat the separation zone of the hydrothermal separation vessel exhibitsa lower density than the concentration zone of the hydrothermalseparation vessel, to cause the contaminants to separate from thesolution in the separation zone and to form a product stream; removingthe product stream from the separation zone of the hydrothermalseparation vessel; and removing the contaminants from the concentrationzone of the hydrothermal separation vessel.

Clause 2: The process of clause 2, wherein the separation zone ismaintained at a pressure greater than 22.1 MPa and a temperature greaterthan 374° C.

Clause 3: The process of clause 1 or 2, wherein the hydrothermalseparation vessel includes a mid-level, mixing zone located between theseparation zone and the concentration zone, wherein the contaminatedfeedstock and the water are each separately fed into the mixing zone,and wherein sufficient shear and mixing is provided in the mixing zoneto cause dissolution of any soluble components of the feedstock into thesupercritical water and separation of the contaminants as insolublecomponents.

Clause 4: The process of any of clauses 1-3, wherein the contaminatedfeedstock and supercritical water are mixed together prior to deliveryto the hydrothermal separation vessel.

Clause 5: The process of any of clauses 1-4, wherein the contaminatedfeedstock is preheated indirectly prior to mixing with the supercriticalwater or is heated directly by mixing with the supercritical water.

Clause 6: The process of any of clauses 1-5, wherein the separation zoneof the hydrothermal separation vessel is configured to achieve up-flowof the supercritical water and any dissolved portions of the feedstock.

Clause 7: The process of any of clauses 1-6, wherein dimensions of thehydrothermal separation vessel and feed rates of the supercritical waterand contaminated feedstock are controlled to result in a verticalvelocity that is less than a gravity settling rate of the contaminants.

Clause 8: The process of clause 7, wherein the vertical velocity in thehydrothermal separation vessel is between 0.1 and 10 feet per minute.

Clause 9: The process of any of clauses 1-8, wherein the densitygradient in the hydrothermal separation vessel results in plug flow inthe vessel.

Clause 10: The process of any of clauses 1-9, wherein a temperature inthe separation zone of the hydrothermal separation vessel is between380° C. and 450° C., or up to the highest temperature that can beachieved without causing thermal cracking, coking, or reaction of thefeedstock.

Clause 11: The process of clause 10, wherein the temperature in theseparation zone of the hydrothermal separation vessel is maintaineddirectly by introduction of supercritical water to the hydrothermalseparation vessel or indirectly by internal or external heat exchangersor heaters applied to the hydrothermal separation vessel.

Clause 12: The process of any of clauses 1-11, wherein a temperature inthe concentration zone is maintained below a reaction temperature of thecontaminants and above a pour point temperature of the contaminants.

Clause 13: The process of any of clauses 1-12, wherein the productstream is continually removed from the hydrothermal separation vesseland the contaminants are continually removed from the concentration zoneof the hydrothermal separation vessel.

Clause 14: The process of any of clauses 1-13, wherein a ratio ofsupercritical water-to-feedstock is between 1:10 to 3:1.

Clause 15: The process of any of clauses 1-14, wherein the contaminatedfeedstock comprises petroleum crude oils, bitumen, petroleum refinerystreams, waste or reclaimed oils and/or crude oil storage tank residue;renewable oils; soaps, algae and/or algal oil, and pyrolysis oil; andthe contaminants comprise coke or mineral particulates, asphaltenes,catalyst fines, resins, salts, metals, and/or minerals.

Clause 16: The process of any of clauses 1-15, wherein the temperaturein the hydrothermal separation vessel is controlled by supplying splitstreams of supercritical water and/or split streams of heatedcontaminated feedstock at differing locations along a vertical height ofthe hydrothermal separation vessel between the separation zone and theconcentration zone.

Clause 17: The process of any of clauses 1-16, including the addition ofseparation aids to selectively enhance the separation and recovery ofhigh molecular weight, non-paraffinic hydrocarbons or to selectivelyenhance the separation and removal of polar contaminants.

Clause 18: A system for separating contaminants from a contaminatedfeedstock comprised of: a hydrothermal separation vessel including atleast one inlet for receiving a feedstock and a supercritical water,said hydrothermal separation vessel including an upper separation zone,a bottom concentration zone, and a mid-level mixing zone located betweenthe separation zone and the concentration zone; a mixing device forcombining the contaminated feedstock and the supercritical water to forma solution, wherein said mixing device is positioned inline prior to theat least one inlet of the hydrothermal separation vessel or positionedwithin the hydrothermal separation vessel, wherein said hydrothermalseparation vessel, feedstock, and supercritical water cooperate togetherto achieve a vertical density gradient within the hydrothermalseparation vessel, wherein the separation zone of the hydrothermalseparation vessel exhibits lower density than the concentration zone ofthe hydrothermal separation vessel to cause the contaminants to separatefrom the solution in the separation zone and to form a product stream;at least one outlet for removing the product stream from the separationzone of the hydrothermal separation vessel; and at least one outlet forremoving the contaminants from the concentration zone of thehydrothermal separation vessel.

Clause 19: The system of clause 18 including multiple inlets within thehydrothermal separation vessel for receiving split streams ofsupercritical water and/or split streams of heated contaminatedfeedstock therein, wherein the multiple inlets are located at varyingvertical heights between the separation zone and the concentration zoneof the hydrothermal reactor to control the temperature of thehydrothermal separation vessel.

Clause 20: The system of clause 18 or 19, wherein the temperature in theseparation zone of the hydrothermal separation vessel is between 380° C.and 450° C., or up to the highest temperature that can be achievedwithout causing thermal cracking, coking, or reaction of the feedstock,and the temperature in the concentration zone is maintained below areaction temperature of the contaminants and above a pour pointtemperature of the contaminants.

Although the invention has been described in detail for the purpose ofillustration based on what is currently considered to be the mostpractical and preferred embodiments, it is to be understood that suchdetail is solely for that purpose and that the invention is not limitedto the disclosed embodiments, but, on the contrary, is intended to covermodifications and equivalent arrangements that are within the spirit andscope of this description. For example, it is to be understood that thepresent invention contemplates that, to the extent possible, one or morefeatures of any embodiment can be combined with one or more features ofany other embodiment.

Whereas particular embodiments of this invention have been describedabove for purposes of illustration, it will be evident to those skilledin the art that numerous variations of the details of the presentinvention may be made without departing from the invention as defined inthe appended claims.

The invention claimed is:
 1. A process for separating contaminants froma contaminated feedstock comprised of: combining a contaminatedfeedstock and supercritical water to form a supercritical water andfeedstock solution in a hydrothermal separation vessel, saidhydrothermal separation vessel including an upper separation zone and abottom concentration zone; maintaining a temperature and pressure withinthe hydrothermal separation vessel to achieve a vertical densitygradient therein such that the separation zone of the hydrothermalseparation vessel exhibits a lower density than the concentration zoneof the hydrothermal separation vessel, to cause the contaminants toseparate from the solution in the separation zone and to form a productstream; removing the product stream from the separation zone of thehydrothermal separation vessel; and removing the contaminants from theconcentration zone of the hydrothermal separation vessel, wherein thehydrothermal separation vessel includes a mid-level, mixing zone locatedbetween the separation zone and the concentration zone, wherein thecontaminated feedstock and the water are each separately fed into themixing zone, and wherein sufficient shear and mixing is provided in themixing zone to cause dissolution of any soluble components of thefeedstock into the supercritical water and separation of thecontaminants as insoluble components.
 2. The process of claim 1, whereinthe separation zone is maintained at a pressure greater than 22.1 MPaand a temperature greater than 374° C.
 3. The process of claim 1,wherein the contaminated feedstock and supercritical water are mixedtogether prior to delivery to the hydrothermal separation vessel.
 4. Theprocess of claim 1, wherein the contaminated feedstock is preheatedindirectly prior to mixing with the supercritical water or is heateddirectly by mixing with the supercritical water.
 5. The process of claim1, wherein the separation zone of the hydrothermal separation vessel isconfigured to achieve up-flow of the supercritical water and anydissolved portions of the feedstock.
 6. The process of claim 1, whereindimensions of the hydrothermal separation vessel and feed rates of thesupercritical water and contaminated feedstock are controlled to resultin a vertical velocity that is less than a gravity settling rate of thecontaminants.
 7. The process of claim 6, wherein the vertical velocityin the hydrothermal separation vessel is between 0.1 and 10 feet perminute.
 8. The process of claim 1, wherein the density gradient in thehydrothermal separation vessel results in plug flow in the vessel. 9.The process of claim 1, wherein a temperature in the separation zone ofthe hydrothermal separation vessel is between 380° C. and 450° C., or upto the highest temperature that can be achieved without causing thermalcracking, coking, or reaction of the feedstock.
 10. The process of claim9, wherein the temperature in the separation zone of the hydrothermalseparation vessel is maintained directly by introduction ofsupercritical water to the hydrothermal separation vessel or indirectlyby internal or external heat exchangers or heaters applied to thehydrothermal separation vessel.
 11. The process of claim 1, wherein atemperature in the concentration zone is maintained below a reactiontemperature of the contaminants and above a pour point temperature ofthe contaminants.
 12. The process of claim 1, wherein the product streamis continually removed from the hydrothermal separation vessel and thecontaminants are continually removed from the concentration zone of thehydrothermal separation vessel.
 13. The process of claim 1, wherein avolume ratio of supercritical water-to-feedstock is between 1:10 to 3:1.14. The process of claim 1, wherein the contaminated feedstock comprisespetroleum crude oils, bitumen, petroleum refinery streams, waste orreclaimed oils and/or crude oil storage tank residue; renewable oils;soaps, algae and/or algal oil, and pyrolysis oil; and the contaminantscomprise coke or mineral particulates, asphaltenes, catalyst fines,resins, salts, metals, and/or minerals.
 15. A process for separatingcontaminants from a contaminated feedstock comprised of: combining acontaminated feedstock and supercritical water to form a supercriticalwater and feedstock solution in a hydrothermal separation vessel, saidhydrothermal separation vessel including an upper separation zone and abottom concentration zone; maintaining a temperature and pressure withinthe hydrothermal separation vessel to achieve a vertical densitygradient therein such that the separation zone of the hydrothermalseparation vessel exhibits a lower density than the concentration zoneof the hydrothermal separation vessel, to cause the contaminants toseparate from the solution in the separation zone and to form a productstream; removing the product stream from the separation zone of thehydrothermal separation vessel; and removing the contaminants from theconcentration zone of the hydrothermal separation vessel, wherein thetemperature in the hydrothermal separation vessel is controlled bysupplying split streams of supercritical water and/or split streams ofheated contaminated feedstock at differing locations along a verticalheight of the hydrothermal separation vessel between the separation zoneand the concentration zone.
 16. The process of claim 1, including theaddition of separation aids.
 17. A system for separating contaminantsfrom a contaminated feedstock comprised of: a hydrothermal separationvessel including at least one inlet for receiving a feedstock and asupercritical water, said hydrothermal separation vessel including anupper separation zone, a bottom concentration zone, and a mid-levelmixing zone located between the separation zone and the concentrationzone, wherein the contaminated feedstock and the water are eachseparately fed into the mixing zone, and wherein sufficient shear andmixing is provided in the mixing zone to cause dissolution of anysoluble components of the feedstock into the supercritical water andseparation of the contaminants as insoluble components; a mixing devicefor combining the contaminated feedstock and the supercritical water toform a solution, wherein said mixing device is positioned inline priorto the at least one inlet of the hydrothermal separation vessel orpositioned within the hydrothermal separation vessel, wherein saidhydrothermal separation vessel, feedstock, and supercritical watercooperate together to achieve a vertical density gradient within thehydrothermal separation vessel, wherein the separation zone of thehydrothermal separation vessel exhibits lower density than theconcentration zone of the hydrothermal separation vessel to cause thecontaminants to separate from the solution in the separation zone and toform a product stream; at least one outlet for removing the productstream from the separation zone of the hydrothermal separation vessel;and at least one outlet for removing the contaminants from theconcentration zone of the hydrothermal separation vessel.
 18. A systemfor separating contaminants from a contaminated feedstock comprised of:a hydrothermal separation vessel including at least one inlet forreceiving a feedstock and a supercritical water, said hydrothermalseparation vessel including an upper separation zone, a bottomconcentration zone, and a mid-level mixing zone located between theseparation zone and the concentration zone; a mixing device forcombining the contaminated feedstock and the supercritical water to forma solution, wherein said mixing device is positioned inline prior to theat least one inlet of the hydrothermal separation vessel or positionedwithin the hydrothermal separation vessel, wherein said hydrothermalseparation vessel, feedstock, and supercritical water cooperate togetherto achieve a vertical density gradient within the hydrothermalseparation vessel, wherein the separation zone of the hydrothermalseparation vessel exhibits lower density than the concentration zone ofthe hydrothermal separation vessel to cause the contaminants to separatefrom the solution in the separation zone and to form a product stream;at least one outlet for removing the product stream from the separationzone of the hydrothermal separation vessel; and at least one outlet forremoving the contaminants from the concentration zone of thehydrothermal separation vessel, the system including multiple inletswithin the hydrothermal separation vessel for receiving split streams ofsupercritical water and/or split streams of heated contaminatedfeedstock therein, wherein the multiple inlets are located at varyingvertical heights between the separation zone and the concentration zoneof the hydrothermal reactor to control the temperature of thehydrothermal separation vessel.
 19. The system of claim 18, wherein thehydrothermal separation vessel is configured to be operated in theseparation zone at a temperature between 380° C. and 450° C., or up tothe highest temperature that can be achieved without causing thermalcracking, coking, or reaction of the feedstock, and the hydrothermalseparation vessel is configured to be maintained in the concentrationzone at a temperature below a reaction temperature of the contaminantsand above a pour point temperature of the contaminants.